OP-20-G or "Office of Chief Of Naval Operations (OPNAV), 20th Division of the Office of Naval Communications, G Section / Communications Security", was the U.S. Navy's signals intelligence and cryptanalysis group during World War II. Its mission was to intercept, decrypt, and analyze naval communications from Japanese, German, and Italian navies. In addition OP-20-G also copied diplomatic messages of many foreign governments. The majority of the section's effort was directed towards Japan and included breaking the early Japanese "Blue" book fleet code. This was made possible by intercept and High Frequency Direction Finder (HFDF) sites in the Pacific, Atlantic, and continental U.S., as well as a Japanese telegraphic code school for radio operators in Washington, D.C.
Prewar The Code and Signal Section was formally made a part of the Division of Naval Communications (DNC), as Op-20-G, on July 1, 1922. In January 1924, a 34-year-old U.S. Navy lieutenant named Laurance F. Safford was assigned to expand OP-20-G's domain to radio interception. He worked out of Room 2646, on the top floor of the Navy Department building in Washington, D.C. Japan was of course a prime target for radio interception and cryptanalysis, but there was the problem of finding personnel who could speak Japanese. The Navy had a number of officers who had served in a diplomatic capacity in Japan and could speak Japanese fluently, but there was a shortage of radiotelegraph operators who could read Japanese Wabun code communications sent in kana. Fortunately, a number of US Navy and Marine radiotelegraph operators operating in the Pacific had formed an informal group in 1923 to compare notes on Japanese kana transmissions. Four of these men became instructors in the art of reading kana transmissions when the Navy began conducting classes in the subject in 1928. The classes were conducted by the Room 2646 crew, and the radiotelegraph operators became known as the "On-The-Roof Gang". By June 1940, OP-20-G included 147 officers, enlisted men, and civilians, linked into a network of radio listening posts as far-flung as the Army's. OP-20-G did some work on Japanese diplomatic codes, but the organization's primary focus was on Japanese military codes. The US Navy first got a handle on Japanese naval codes in 1922, when Navy agents broke into the Japanese consulate in New York City, cracked the safe, took photographs of pages of a Japanese navy codebook, and left, having put everything back as they had found it. Before the war, the Navy cipher bureau operated out of three main bases:
Station NEGAT at headquarters in Washington, D.C. Station HYPO (or FRUPAC), a section at Pearl Harbor in Hawaii Station CAST, a section in the fortified caves of the island of Corregidor, in the Philippines, with codebreakers and a network of listening and radio direction finding stations. FRUMEL was established in Melbourne when Navy signals intelligence personnel from the Philippines were evacuated to Australia. Evacuated Army signals intelligence personnel went to the Central Bureau. The US Army Signal Intelligence Service (SIS) and OP-20-G were hobbled by bureaucracy and rivalry, competing with each other to provide their intelligence data, codenamed "MAGIC", to high officials. Complicating matters was that the Coast Guard, the FBI, and even the FCC also had radio-intercept operations. The Navy organization at OP-20-G was more conventionally hierarchical than the Army at Arlington Hall which went more on merit rather than rank (like Bletchley Park), though commissions were handed out to "civilians in uniform" with rank according to age (an ensign for 28 or under, a lieutenant to 35 or a lieutenant commander if over 35). But control was by "regular military types". The Navy wanted the Army to forbid civilians to touch the SIGABA cipher machine like the Navy; though it was developed by a civilian (William Friedman). A Royal Navy visitor and intercept specialist Commander Sandwith reported in 1942 on "the dislike of Jews prevalent in the US Navy (while) nearly all the leading Army cryptographers are Jews". In 1940, SIS and OP-20-G came to agreement with guide lines for handling MAGIC; the Army was responsible on even-numbered days and the Navy on odd-numbered days. So, on the first minute after midnight on 6 December 1941 the Navy took over. But USN Lt-Comdr Alwin Kramer had no relief officer (unlike the Army, with Dusenbury and Bratton); and that night was being driven around by his wife. He was also responsible for distributing MAGIC information to the President; in January 1941 the Army agreed that they would supply the White House in January, March, May, July, September and November and the Navy in February, April, June, August, October and December. But in May 1941 MAGIC documents were found in the desk of Roosevelt's military aide Edwin "Pa" Watson and the Navy took over; while the Army provided MAGIC to the State Department instead. The result was that much of the MAGIC intelligence was delayed or unused. There was no efficient process for assessing and organizing the intelligence, as was provided postwar by a single intelligence agency.
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